Robotic, or automatic, welders accurately perform welding operations which would be difficult and/or time consuming if performed by a human. Human welders can visually perceive the area of the welding operation, the location of the elements to be welded, and compensate for the misalignment of the elements. However, robotic welders do not have such intelligence and need information about the workpiece, such as the coordinates of the elements to be welded, any elements which must be worked around, etc. This information is generally provided by a human, at least to some degree. For example, a human operator may, using manual controls, move the robotic welder sensing arm about the workpiece and instruct the robotic welder to store the coordinates of the bottom plate, an intersection of elements, a corner, etc. Also, the robotic welder can accept information about the ideal element locations from a computer assisted design (CAD) program which was used to draw the plans for the workpiece to be welded.
Elements may not be always placed in their "ideal" locations, they may be offset or skewed In many cases, this offset or skew does not affect the structural-integrity of the finished product as long as the offset or skew is within certain, usually generous, tolerances.
A robotic welder, especially one which has a "touch-sense" feature, can compensate for some offset or skew. However, if the offset or skew exceeds a certain amount then the robotic welder may start outside a compartment, rather than within it, and thereby perform the wrong welding operation.
Therefore, there is a need for a method which accurately determines the locations of the elements, as placed, so that the configuration of the workpiece will be accurately known by the robotic welder.